Semiconductor interconnect structure and manufacturing method thereof

ABSTRACT

The present disclosure provides an interconnect structure, including a low k dielectric layer with an air gap region and a non-air gap region. A first conductive line is positioned in the air gap region, and a second conductive line is positioned in the non-air gap region of the low k dielectric layer. A height of the first conductive line is different from a height of the second conductive line. The present disclosure also provides a method for manufacturing a semiconductor interconnect structure, including forming a photoresist layer over a hard mask layer with openings exposing a low k dielectric layer; treating the low k dielectric layer to be more hydrophilic through the openings of the hard mask layer; and removing the treated low k dielectric region to form an air gap in the air gap region.

BACKGROUND

Semiconductor integrated circuit (IC) industry has experienced rapidgrowth. Technological advances in IC materials and design have producedgenerations of ICs where each generation has smaller and more complexcircuits than the previous generation. However, these advances haveincreased the complexity of processing and manufacturing ICs and, forthese advances to be realized, similar developments in IC processing andmanufacturing are needed.

In the course of IC evolution, functional density (i.e., the number ofinterconnected devices per chip area) has generally increased whilegeometry size (i.e., the smallest component (or line) that can becreated using a fabrication process) has decreased. This scaling downprocess generally provides benefits by increasing production efficiencyand lowering associated costs. Such scaling-down also produces arelatively high power dissipation value, which may be addressed by usinglow power dissipation devices such as complementarymetal-oxide-semiconductor (CMOS) devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a cross sectional view of an interconnect structure withlocalized air gap, in accordance with some embodiments of the presentdisclosure.

FIG. 2 is a cross sectional view of an interconnect structure withlocalized air gap, in accordance with some embodiments of the presentdisclosure.

FIG. 3 is a cross sectional view of an interconnect structure withlocalized air gap, in accordance with some embodiments of the presentdisclosure.

FIG. 4 is a cross sectional view of an interconnect structure withlocalized air gap, in accordance with some embodiments of the presentdisclosure.

FIG. 5 is a cross sectional view of an interconnect structure withlocalized air gap, in accordance with some embodiments of the presentdisclosure.

FIGS. 6A, 6B, 6C, 7, 9A, 9B, 11A, 12A are cross sectional views ofoperations for manufacturing an interconnect structure with localizedair gap, in accordance with some embodiments of the present disclosure.

FIGS. 6A, 6B, 6C, 8, 10A, 10B, 11B, 12B are cross sectional views ofoperations for manufacturing an interconnect structure with localizedair gap, in accordance with some embodiments of the present disclosure.

FIG. 13A is a cross sectional view of an interconnect structure withlocalized air gap, in accordance with some embodiments of the presentdisclosure.

FIG. 13B is a cross sectional view of an interconnect structure withlocalized air gap, in accordance with some embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In semiconductor manufacturing, a low K dielectric is a material with asmall dielectric constant relative to silicon dioxide. Low K dielectricmaterial implementation is one of several strategies used to allowcontinued scaling of microelectronic devices. In integrated circuits,insulating dielectrics separate the conducting parts (i.e., wireinterconnects) from one another. As components have scaled andtransistors have been fabricated closer together, the insulatingdielectrics have thinned to the point where charges build up andcrosstalk may, in some instance, adversely affect the performance of thedevice. Replacing the traditional silicon dioxide dielectric layers witha low K dielectric of the same thickness reduces parasitic capacitance,thus enabling faster switching speeds and lower heat dissipation.

Traditional dielectric layers such as silicon dioxide have a relativelyhigh dielectric constant of about 3.9, while some other materials suchas fluorine silicon oxide have a dielectric constant of about 3.7. Aclass of materials typically referred to as low K dielectric materialshave a dielectric constant of about 3.0 or lower, while a dielectricconstant of 2.0 or less is deemed to an ultra low K dielectric material.Air, on the other hand, has a dielectric constant of 1.0. Strategies touse various low K dielectric materials suffer from poor mechanicalproperties, poor adhesion, difficult integration, and poor defectcontrol. A universal air gap maximizes the volume of low K dielectricmaterials but generates serious via landing problem. Conductive viaspositioned on a layer higher than the universal air gap suffer poormechanical support. In addition, tolerance to the misalignment of theupper layer conductive vias is small in the universal air gap low kdielectric structure.

Localized air gap somehow provides a larger landing area for the upperlayer conductive vias. An additional lithography operation is conductedto remove the low k dielectric layer in a predetermined and localizedregion. However, the extra plasma dry etch operation imposed to removethe low k dielectric layer inevitably damages the metal lines positionedin the air gap region. Subsequent operations can further damage themetal lines and thus extra operations shall be conducted to restore themechanical and electrical properties of the metal lines, in order topass the interconnect reliability test.

The present disclosure provides an interconnect structure with localizedair gap but the integrity of the metal line positioned in the air gapregion is not deteriorated during the manufacturing operations. In someembodiments, the metal lines in the air gap region and in the non-airgap region can have different heights. Since the air gap region islocalized, the via landing overlay problems can be solved.

The present disclosure provides a manufacturing method for preparing aninterconnect structure with localized air gap. The method providedherein does not include further lithography operations for the formationof the localized air gap after the metal line is deposited.Consequently, no further damages to the metal lines during subsequentlithography operations. Hence, the integrity of the metal lines can beprotected in a better condition compared to those metal lines preparedby conventional operations, where a dry etch operation is imposedthrough a patterned photoresist layer to remove the low k dielectricmaterials surrounding the metal lines and form the air gap. Furthermore,the exposed metal lines are subjected to chemical damages forphotoresist stripping.

Referring to FIG. 1, a cross sectional view of an interconnect structure10 with an air gap 101A′ is shown. Air gap 101A′ is a localized air gapaccommodating first conductive lines 103. In some embodiments, the firstconductive lines 103 and the air gap 101A's are collectively referred toan air gap region 101A of a dielectric layer 101. The dielectric layer101 is positioned over a substrate 100. In some embodiments, theinterconnect structure 10 may not include a substrate 100. Adjacent tothe air gap region 101A is a non-air gap region 101B including a secondconductive line 105 surrounded by the dielectric layer 101. In someembodiments, the first conductive line 103 illustrated in theinterconnect structure 10 extends along the Y direction such that abottom 103′ of the first conductive line 103 is in contact with thedielectric layer 101. Similarly, the second conductive line 105 alsoextends along the Y direction. However, in other embodiments, the firstconductive line 103 and/or the second conductive line 105 can beinterconnect vias which electrically connect a conductive region at thebottom (103′ or 105′) to another conductive line or external circuits atthe other end of the vias (not shown in FIG. 1).

In some embodiments, the substrate 100 can be an elementarysemiconductor including silicon or germanium in crystal,polycrystalline, or an amorphous structure; a compound semiconductorincluding silicon carbide, gallium arsenic, gallium phosphide, indiumphosphide, indium arsenide, and indium antimonide; an alloysemiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, andGaInAsP; any other suitable material; or combinations thereof. In oneembodiment, the alloy semiconductor substrate may have a gradient SiGefeature in which the Si and Ge composition change from one ratio at onelocation to another ratio at another location of the gradient SiGefeature. In another embodiment, the gradient SiGe feature is formed overa silicon substrate. In yet another embodiment, the gradient SiGefeature is strained. Furthermore, the semiconductor substrate may be asemiconductor on insulator, such as a silicon on insulator (SOI), or athin film transistor (TFT). In some examples, the semiconductorsubstrate may include a doped epitaxial layer or a buried layer. In someother examples, the compound semiconductor substrate may have amultilayer structure, or the substrate may include a multilayer compoundsemiconductor structure.

In some embodiments, the dielectric layer 101 may include at least oneof the following materials, such as carbon-containing silicon oxide,carbon-containing silicon nitride, carbon-containing silicon oxynitride,carbon-containing low-k dielectric material, ultra low-k dielectricmaterial, or any combinations thereof. In some embodiments, thedielectric layer 101 can be made of a low-k dielectric material having adielectric constant k less than or equal to 3, such as Black Diamond®available from Applied Materials, Incorporated®. In some otherembodiments, the dielectric layer 101 may be made of, withoutlimitation, fluorinated silicate glass (FSG) or undoped silicate glass(USG). In still other embodiments, the materials selected for dielectriclayer 101 are susceptible to carbon reduction by anisotropic dry gasplasma chemistries.

In some embodiments, the first conductive line 103 and the secondconductive line 105 include at least one material such as copper (Cu),tungsten (W), aluminum (Al), Al/Cu, graphene, carbon nanotubes (CNT),carbon nanocapsules, other conbon-based or metallic-based conductivematerials, or any combinations thereof. As shown in FIG. 1, a majordirection for the first conductive line 103 and the second conductiveline 105 are defined as the direction perpendicular to a surface of thesubstrate 100, that is, along the Z direction. A height H1 along themajor direction of the first conductive line 103 is greater than aheight H2 along the major direction of the second conductive line 105 bya difference D. In other words, the bottom 103′ of first conductive line103 and the bottom 105′ of second conductive line 105 demonstrate ameasurable shift equivalent to a difference D, regardless of whether thebottom 103′ of the first conductive line 103 is over or under a bottomsurface of the air gap 101A′. In some embodiments, the difference D canbe in a range of from about 10% to about 50% of the height H1.

The first conductive line 103 and the second conductive line 105 can bedistinguished by the region they respectively reside in. For example,the first conductive line 103 is positioned in the air gap region 101A,whereas the second conductive line 105 is positioned in the non-air gapregion 101B. In addition, a sidewall 103A the first conductive line 103is surrounded by air gap 101A′, while a sidewall 105A of the secondconductive line 105 is surrounded by the dielectric layer 101. In someembodiments, a liner material (not shown) can be formed along thesidewall 105A and the bottom 105′ of the second conductive line 105. Theliner material can include, not in a limited way, silicon nitride,silicon oxynitride (SiON), silicon oxycarbide (SiOC), silicon carbonnitride (SiCN), silicon carbon oxynitride (SiCON), silicon carbide(SiC), other liner materials, or any combinations thereof. Furthermore,the bottom 103′ of the first conductive line 103 can be disposed on abottom surface 151 of the air gap 101A′ as shown in FIG. 1, or be buriedunder the bottom surface 151 of the air gap 101A′ (not shown). In otherwords, the first conductive line 103 can be partially buried in thedielectric layer 101, whereas the second conductive line 105 iscompletely buried in the dielectric layer 101.

Referring to FIG. 2, a cross sectional view of an interconnect structure20A with an air gap 101A′ is shown. Repeated numeral labels shown inFIG. 2 are referred to the same elements or their equivalents in FIG. 1,and are not repeated here for simplicity. In FIG. 2, the secondconductive line 105 of the interconnect structure 20A possesses a heightH2 greater than the height H1 of the first conductive line 103 by adifference D. In some embodiments, the height H2 can be greater than theheight H1. In other embodiments, the height H2 is less than the heightH1. In some embodiments, a ratio of the height H1 and the height H2 isin a range of from about 0.8 (for embodiments with H2>H1) to about 1.5(for embodiments with H1>H2).

Referring again to FIG. 2, a cap layer 107 is positioned over the airgap region 101A and the non-air gap region 101B of the dielectric layer101. In some embodiments, the cap layer 107 includes ceramics, metaloxynitrides M_(x)O_(y)N_(z), dielectric films, organic polymer films, orthe combinations thereof. The M in M_(x)O_(y)N_(x) refers to metal, forexample, Al, Mn, Co, Ti, Ta, W, Ni, Sn, or Mg. The O refers to oxygenand N refers to nitrogen. In some embodiments, the stoichiometry x, y, zfor M_(x)O_(y)N_(z) can have x in a range of from about 20 to about 70atomic percent, y in a range below 80 atomic percent, and z in a rangebelow 80 atomic percent. In some embodiments, the oxygen and nitrogencontent is greater than the metal content in M_(x)O_(y)N_(z), that is, yand z are greater than x. The dielectric films for the cap layer 107 caninclude SiCN, SiN, SiO₂, SiON, SiOC, or SiOF. In some embodiments, thecap layer 107 possesses a thickness of from about 5 Å to about 50 Å. Theair gap 101A′ shown in FIG. 2 is a closed space and the cap layer 107 isallowed to support more conductive lines to be stacked over theinterconnect structure 20A.

Referring again to FIG. 2, a conformal barrier layer 108 is depositedover the dielectric layer 101 and the first conductive lines 103. Aconformal deposition allows the barrier layer 108 to conform with thesurface morphology of the air gap 101A; and the first conductive lines103. In some embodiments, the conformal barrier layer 108 includesceramics, metal oxynitrides M_(x)O_(y)N_(z), dielectric films, or thecombinations thereof. The M in M_(x)O_(y)N_(z) refers to metal, forexample, Al, Mn, Co, Ti, Ta, W, Ni, Sn, or Mg. The O refers to oxygenand N refers to nitrogen. In some embodiments, the stoichiometry x, y, zfor M_(x)O_(y)N_(z) can have x in a range of from about 20 to about 70atomic percent, y in a range below 80 atomic percent, and z in a rangebelow 80 atomic percent. In some embodiments, the oxygen and nitrogencontent is greater than the metal content in M_(x)O_(y)N_(z), that is, yand z are greater than x. The dielectric films for the conformal barrierlayer 108 can include SiCN, SiN, SiO₂, SiON, SiOC, or SiOF. In someembodiments, the conformal barrier layer 108 possesses a thickness offrom about 5 Å to about 50 Å.

Still referring to FIG. 2, a separation W1 between two adjacent firstconductive lines 103 cannot be too wide otherwise the cap layer 107 maylack of mechanical support and falls into the air gap 101A′. In someembodiments, the separation W1 between two adjacent first conductivelines 103 is lower than about 50 nm. The separation W1 refers to adistance between the sidewalls of two adjacent first conductive lines103 or a distance between the conformal barrier layer 108 formed on thesidewalls of two adjacent first conductive lines 103. In someembodiments, a shortest separation between the first conductive line 103and a sidewall 153 of the air gap 101A′ is lower than about 50 nm.

Referring to FIG. 3, a cross sectional view of an interconnect structure20B with an air gap 101A′ is shown. Repeated numeral labels shown inFIG. 3 are referred to the same elements or their equivalents in FIG. 1and FIG. 2, and are not repeated here for simplicity. A differencebetween the interconnect structure 20A and 20B is in that the conformalbarrier layer 108 in the interconnect structure 20B can be composed ofsubstantially identical materials of the cap layer 107. In someembodiments, the formation of the conformal barrier layer 108 ofstructure 20A is an independent operation conducted prior to theformation of the cap layer 107. However, the formation of the conformalbarrier layer 108 of structure 20 b is the same operation to theformation of the cap layer 107.

Referring to FIG. 4, a cross sectional view of an interconnect structure30 with an air gap 101A′ is shown. Repeated numeral labels shown in FIG.4 are referred to the same elements or their equivalents in FIG. 1 toFIG. 3, and are not repeated here for simplicity. In FIG. 4, a conformalmetal layer 109 is formed only on a top surface 103B and a sidewall 103Aof the first conductive line 103, and a top surface 105B of the secondconductive line 105. In some embodiments, the conformal metal layer 109includes cobalt (Co) and any other suitable metallic materials forselective deposition. Conductive lines 113 and 115 in the upper stack ofthe dielectric layer 111 are illustrated in dotted lines. For example,the conductive line 113 over the air gap region 101A possesses a widthless than that of the first conductive line 103. The conductive line 115over the non-air gap region may have a width more or less than that ofthe second conductive line 105. Moreover, conductive line 115 maypartially overlay on the second conductive line 105.

Referring to FIG. 5, a cross sectional view of an interconnect structure40 with an air gap 101A′ is shown. Repeated numeral labels shown in FIG.5 are referred to the same elements or their equivalents in FIG. 1 toFIG. 4, and are not repeated here for simplicity. The air gap region101A in FIG. 5 includes not only the air gap 101A′, the first conductivelines 103, as well as an internal dielectric layer 102. In someembodiments, the internal dielectric layer 102 is positioned between twoadjacent first conductive lines 103, and is not in contact with the twofirst conductive lines 103. That is, the first conductive lines 103 inthe air gap region 101A are surrounded by air gap 101A′ despite theexistence of the internal dielectric layer 102.

Still referring to FIG. 5, a separation W2 between a sidewall 103A ofthe first conductive line 103 and a sidewall 102A of the internaldielectric layer 102 cannot be too wide otherwise the cap layer 107 maylack of mechanical support and falls into the air gap 101A′. In someembodiments, the largest separation W2 is lower than about 50 nm. Insome embodiments, the internal dielectric layer 102 is in tapered shapewith a shorter end in contact with the cap layer 107, and hence, thelargest separation between the sidewall 103A of the first conductiveline 103 and the sidewall 102A of the internal dielectric layer 102 isthe distance at the top surface of the internal dielectric layer 102. Insome embodiments, when a pitch P between two adjacent first conductivelines 103 is greater than 50 nm, an internal dielectric layer 102 ispositioned between in between.

FIG. 6A to FIG. 12B are cross sectional views of operations formanufacturing an interconnect structure with localized air gap, inaccordance with some embodiments of the present disclosure. Repeatednumeral labels shown therein are referred to the same elements or theirequivalents as previously discussed in the present disclosure, and arenot repeated here for simplicity. Referring to FIGS. 6A, 6B, and 6C, ahard mask layer is patterned over the dielectric layer 101 and thesubstrate 100. In some embodiments, a first hard mask layer 121 ispatterned over the second hard mask layer 122, as shown in FIG. 6A. Thefirst hard mask layer 121 includes openings (121A, 121B, 121C). In FIG.6B, a photoresist layer 123 is subsequently formed over the first hardmask layer 121, exposing openings 121A and 121B situated in thepredetermined air gap region 101A, and covering the opening 121C in thenon-air gap region 101B. An opening 123′ of the photoresist layer 123defines the air gap region 101A as discussed previously in the presentdisclosure. In FIG. 6C, the portion of the second hard mask layer 122exposed from the openings 121A, 121B of the first hard mask layer 121 isremoved. Consequently, a portion of the dielectric layer 101 is exposedfrom the openings 122A, 122B of the second hard mask layer 122.

Referring to FIG. 7, a dielectric layer treatment is conducted throughthe openings 122A, 122B of the second hard mask layer 122. In someembodiments, the dielectric layer treatment is to transform a portion ofthe original dielectric layer 101 to a treated dielectric region 131that has a lateral dimension D_(t) greater than a width D_(A) and D_(B)of the openings (122A, 122B) of the second hard mask layer 122. In otherwords, the lateral dimension D_(t) of the treated dielectric region 131is greater than D_(A)+D_(B.) In some embodiments, the treatment is toobtain a more hydrophilic portion in the dielectric layer 101. Forexample, if the dielectric layer 101 is made of SiOC, microwave plasmacan be used to decrease the carbon content in specific portion of thedielectric layer 101 and replace SiOC with SiOH. The hydrophilicity ofthe treated dielectric region 131 is increased. The treated dielectricregion 131 is hence easier to be etched by wet chemical etch operation,such as by diluted HF.

As shown in FIG. 7, in some embodiments, the dielectric layer treatmentincludes applying microwave plasma 150 to the interconnect structure ina plasma chamber with pressure in a range of from about 100 mTorr toabout 2000 mTorr. The temperature in the chamber is maintained in arange of from about 60° C. to about 300° C., with a plasma gas chemistryincluding nitrogen (N₂), oxygen (O₂), and water (H₂O). In someembodiments, N₂ constitutes 3% to 60%, O₂ constitutes 20% to 98%, andH₂O constitutes 3% to 98% of the gas flow for plasma treatment. In otherembodiments, in addition to N₂, O₂, and H₂O, the plasma gas chemistryalso includes CF₄ which, for example, constitutes below 5% of the gasflow.

Comparing FIG. 7 and FIG. 8, the separation W1 of the two openings(122A, 122B) in FIG. 7 is below 50 nm, for example, 30 nm, and theseparation W1 of the two openings (122A, 122B) in FIG. 8 is greater than50 nm, for example, 80 nm. As such, the treated dielectric region 131 inFIG. 7 shows a continuous region without dielectric layer 101separation, whereas the treated dielectric region 131 in FIG. 8 showstwo individual regions 131A and 131B with dielectric layer 101 inbetween. The plasma treatment described herein induces lateralencroachment to a point that not only the exposed region under theopenings 122A, 122B, but also the portion covered by the hard masklayers 121, 122 that is immediately adjacent to the exposed region, canbe transformed to be more hydrophilic and become a part of the treateddielectric region 131. In some embodiments, the lateral encroachment ofthe treated dielectric region 131 described herein is below about 30 nm.

Referring to FIG. 7, FIG. 9A, and FIG. 9B, the photoresist layer 123 isremoved, and the hard mask layer 122 in the non-air gap region 101B isthen exposed. Conductive line trenches 113A and 113B are formed after ananisotropic etch through the openings 122A, 122B, and 121C. Note in FIG.9A, a height H2 of the conductive line trench 113B is less than theheight H1 of the conductive line trench 113A by a difference D. Relateddiscussion to the difference D can be referred to FIG. 1 of the presentdisclosure. However, the height H2 of the conductive line trench 113Bcan be more than the height H1 of the conductive line trench 113A by adifference D as previously discussed in FIG. 2 and FIG. 3. Differenttreatment used to change the chemical property of the treated dielectricregion 131 can cause a faster or a slower etch rate in the treateddielectric region 131 than the dielectric layer 101. As shown in FIG.9A, the etch rate of the treated dielectric region 131 in the air gapregion 101A is faster than the etch rate of the dielectric layer 101 inthe non-air gap region 101B. In some embodiments, the difference D canbe caused by etching an extra second hard mask layer 122 exposed fromthe opening 121C after the removal of the photoresist layer 123, whilethe anisotropic etch for creating the conductive line trenches 113A,113B is in progress. FIG. 9B shows a metallization operation that fillsthe conductive line trenches 113A, 113B with conductive materials andforms the first conductive line 103 and the second conductive line 105.In some embodiments, the metallization operation includes chemical vapordeposition, physical vapor deposition, coating, electroplating, or thecombination thereof. A planarization operation may follow themetallization operation to expose the treated dielectric region 131.

Referring to FIG. 8, FIG. 10A, and FIG. 10B, the photoresist layer 123is removed, and the hard mask layer 122 in the non-air gap region 101Bis then exposed. Conductive line trenches 113A and 113B are formed afteran anisotropic etch through the openings 122A, 122B, and 121C. Note inFIG. 10A, a height H2 of the conductive line trench 113B is less thanthe height H1 of the conductive line trench 113A by a difference D.Related discussion to the difference D can be referred to FIG. 1 of thepresent disclosure. However, the height H2 of the conductive line trench113B can be more than the height H1 of the conductive line trench 113Aby a difference D as previously discussed in FIG. 2 and FIG. 3.Different treatment used to change the chemical property of the treateddielectric region 131 can cause a faster or a slower etch rate in thetreated dielectric region 131 than the dielectric layer 101. As shown inFIG. 10A, the etch rate of the treated dielectric region 131 in the airgap region 101A is faster than the etch rate of the dielectric layer 101in the non-air gap region 101B. In some embodiments, the difference Dcan be caused by etching an extra second hard mask layer 122 exposedfrom the opening 121C after the removal of the photoresist layer 123,while the anisotropic etch for creating the conductive line trenches113A, 113B is in progress. FIG. 10B shows a metallization operation thatfills the conductive line trenches 113A, 113B with conductive materialsand forms the first conductive line 103 and the second conductive line105. In some embodiments, the metallization operation includes chemicalvapor deposition, physical vapor deposition, coating, electroplating, orthe combination thereof. A planarization operation may follow themetallization operation to expose the treated dielectric region 131.

Referring to FIG. 9B, FIG. 10B, FIG. 11A, and FIG. 11B, the treateddielectric region 131 is removed by fluoride-containing chemical etch,such as a diluted HF wet etch. An air gap 101A′ is defined after theremoval of the treated dielectric region 131. In some embodiments,corrosion inhibitor such as suitable organic materials that includes ahydrophilic end and a hydrophobic end can be added to the chemicaletchant to prevent damage to the first conductive line 103. In someembodiments, metal inhibitor can be Bezotrialole which inhibitscorrosion of copper by forming an inert layer of this polymer on themetal's surface. As shown in FIG. 11A, a continuous air gap 101A′ isformed, surrounding the first conductive lines 103, whereas in FIG. 11B,two individual air gaps 101A′ are formed. Because no treated dielectricregion is formed in proximity to the second conductive line 105, no airgap is formed near the second conductive line 105.

Referring to FIG. 12A to FIG. 13B, a cap layer 107 having a thickness offrom about 5 Å to about 50 Å is formed over the air gap region 101A andthe non-air gap region 101B. In some embodiments, the cap layer 107 isformed by conducting a chemical vapor deposition (CVD), physical vapordeposition (PVD), remote plasma CVD (RPCVD), plasma enhanced CVD(PECVD), a coating operation, or other suitable deposition processes.The materials used for the cap layer 107 are previously discussed inFIG. 2.

In FIG. 12A and FIG. 12B, a conformal barrier layer 108 having athickness of from about 5 Å to about 50 Å is formed in the air gap 101A′by an atomic layer deposition (ALD). The conformal barrier layer 108covers the sidewall and the bottom of the air gap 101A, as well as thesidewall 103A and the top surface 103B of the first conductive line 103.In some embodiments, the cap layer 107 and the conformal barrier layer108 are formed in a single deposition operation. For example, as shownin FIG. 12A, the conformal barrier layer 108 is the initial depositionof the cap layer 107 formation before the film laterally coalescence. Inanother example, as shown in FIG. 12B, the cap layer 107 and theconformal barrier layer 108 are made of different materials and areformed in two different operations.

Referring to FIG. 13A and FIG. 13B, a metal layer 109 is selectivelyformed over the first conductive lines 103 and the second conductiveline 105. In some embodiments, the metal layer 109 is formed byconducting a chemical vapor deposition (CVD), remote plasma CVD (RPCVD),plasma enhanced CVD (PECVD), or other suitable deposition processes. Thematerials suitable for the metal layer 109 are previously discussed inFIG. 4. Because the metal layer 109 only selectively deposited overconductive surface, only the sidewall 103A, the top surface 103B of thefirst conductive line 103, and the top surface 105B of the secondconductive line 105 are covered with the metal layer 109.

Some embodiments of the present disclosure provides an interconnectstructure including a substrate and a low k dielectric layer. The low kdielectric layer has an air gap region and a non-air gap region. A firstconductive line is positioned in the air gap region, and a secondconductive line is positioned in the non-air gap region of the low kdielectric layer. A major direction of the first conductive line and amajor direction of the second conductive line are substantiallyperpendicular to the substrate. A height of the first conductive linealong the major direction of the first conductive line is different froma height of the second conductive line along the major direction of thesecond conductive line.

In some embodiments of the present disclosure, a ratio of the height ofthe first conductive line and the height of the second conductive lineis in a range of from about 0.8 to about 1.5.

In some embodiments of the present disclosure, a separation between twoadjacent first conductive lines is less than about 50 nm.

In some embodiments of the present disclosure, further including a caplayer over the air gap region of the low k dielectric layer.

In some embodiments of the present disclosure, further including aconformal barrier layer over the low k dielectric layer and the firstconductive line.

In some embodiments of the present disclosure, materials of the caplayer are substantially the same as materials of the conformal barrierlayer.

In some embodiments of the present disclosure, further including aconformal metal layer over a top surface and a sidewall of the firstconductive line

In some embodiments of the present disclosure, further including aninternal low k material between two adjacent first conductive lines.

In some embodiments of the present disclosure, a largest separationbetween a sidewall of the first conductive line and the internal low kmaterial is below about 50 nm.

Some embodiments of the present disclosure provides a semiconductorinterconnect structure, including a substrate, a low k dielectric layerover the substrate, an air gap in the low k dielectric layer, a firstconductive line and a second conductive line. The first conductive lineis in the low k dielectric layer and is surrounded by the air gap. Thesecond conductive line is in the low k dielectric layer and issurrounded by the low k dielectric layer. A bottom of the firstconductive line is lower than a bottom of the second conductive line.

In some embodiments of the present disclosure, further including aconformal barrier layer made of ceramics, metal oxynitride, dielectricfilm, or a combination of the above materials.

In some embodiments of the present disclosure, further including a caplayer over the air gap. The cap layer is made of ceramics, metaloxynitride, dielectric film, organic polymer films, or the combinationof the above materials.

Some embodiments of the present disclosure provide a method formanufacturing a semiconductor interconnect structure. The methodincludes (1) forming a photoresist layer over a hard mask layer withopenings exposing a low k dielectric layer. The photoresist layerexposing a predetermined air gap region of the low k dielectric layer;(2) Treating the low k dielectric layer to be more hydrophilic throughthe openings of the hard mask layer, and obtaining a treated low kdielectric region with a greater lateral dimension than a width of theopenings of the hard mask layer; (3) Removing a portion of the treatedlow k dielectric region through the openings of the hard mask layer toform a conductive line trench; (4) Metalizing the conductive line trenchto form a conductive line; and (5) removing the treated low k dielectricregion to form an air gap in the air gap region.

In some embodiments of the present disclosure, the treating the low kdielectric layer includes reducing carbon content in the low kdielectric layer.

In some embodiments of the present disclosure, the treating the low kdielectric layer includes applying microwave plasma under a pressure offrom about 200 mTorr to about 2000 mTorr.

In some embodiments of the present disclosure, the microwave plasmaincludes nitrogen, oxygen, water, and optionally fluoride gas.

In some embodiments of the present disclosure, the removing the treatedlow k dielectric region includes applying a fluoride-based wet etch.

In some embodiments of the present disclosure, the method furtherincludes forming a cap layer over the air gap region by a chemical vapordeposition, a physical vapor deposition, a coating operation, or acombination of the above operations.

In some embodiments of the present disclosure, the method furtherincludes forming a conformal barrier layer in the air gap by an atomiclayer deposition (ALD) operation.

In some embodiments of the present disclosure, the method furtherincludes selectively forming a metal layer over the conductive line.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An interconnect structure, comprising: a low kdielectric layer over a substrate, comprising an air gap region and anon-air gap region; a first conductive line in the air gap region; and asecond conductive line in the non-air gap region, wherein a majordirection of the first conductive line and a major direction of thesecond conductive line are substantially perpendicular to the substrate,and a height of the first conductive line along the major directionthereof is different from a height of the second conductive line alongthe major direction thereof.
 2. The interconnect structure of claim 1, aratio of the height of the first conductive line and the height of thesecond conductive line is in a range of from about 0.8 to about 1.5. 3.The interconnect structure of claim 1, a separation between two adjacentfirst conductive lines is less than about 50 nm.
 4. The interconnectstructure of claim 1, further comprising a cap layer over the air gapregion of the low k dielectric layer.
 5. The interconnect structure ofclaim 4, further comprising a conformal barrier layer over the low kdielectric layer and the first conductive line.
 6. The interconnectstructure of claim 5, wherein materials of the cap layer aresubstantially the same as materials of the conformal barrier layer. 7.The interconnect structure of claim 1, further comprising a conformalmetal layer over a top surface and a sidewall of the first conductiveline.
 8. The interconnect structure of claim 6, further comprising aninternal low k material between two adjacent first conductive lines. 9.The interconnect structure of claim 8, a largest separation between asidewall of the first conductive line and the internal low k material isbelow about 50 nm.
 10. A semiconductor interconnect structure,comprising: a low k dielectric layer over a substrate; an air gap in thelow k dielectric layer; a first conductive line in the low k dielectriclayer, surrounded by the air gap; and a second conductive line in thelow k dielectric layer, surrounded by the low k dielectric layer;wherein a bottom of the first conductive line is lower than a bottom ofthe second conductive line.
 11. The interconnect structure of claim 10,further comprising a conformal barrier layer made of ceramics, metaloxynitride, dielectric film, or a combination thereof.
 12. Theintegrated circuit structure of claim 10, further comprising a cap layerover the air gap, composed of ceramics, metal oxynitride, dielectricfilm, organic polymer films, or the combination thereof.
 13. A methodfor manufacturing a semiconductor interconnect structure, comprising:forming a photoresist layer over a hard mask layer with openingsexposing a low k dielectric layer, the photoresist layer exposing apredetermined air gap region of the low k dielectric layer; treating thelow k dielectric layer to be more hydrophilic through the openings ofthe hard mask layer and obtaining a treated low k dielectric region witha greater lateral dimension than a width of the openings of the hardmask layer; removing a portion of the treated low k dielectric regionthrough the openings of the hard mask layer to form a conductive linetrench; metalizing the conductive line trench to form a conductive line;and removing the treated low k dielectric region to form an air gap inthe air gap region.
 14. The method of claim 13, wherein the treating thelow k dielectric layer comprises reducing carbon content in the low kdielectric layer.
 15. The method of claim 13, wherein the treating thelow k dielectric layer comprises applying microwave plasma under apressure of from about 200 mTorr to about 2000 mTorr.
 16. The method ofclaim 15, wherein the microwave plasma comprises nitrogen, oxygen,water, and optionally fluoride gas.
 17. The method of claim 13, whereinthe removing the treated low k dielectric region comprises applying afluoride-based wet etch.
 18. The method of claim 13, further comprisingforming a cap layer over the air gap region by a chemical vapordeposition, a physical vapor deposition, a coating operation, or acombination thereof.
 19. The method of claim 13, further comprisingforming a conformal barrier layer in the air gap by an atomic layerdeposition (ALD) operation.
 20. The method of claim 13, furthercomprising selectively forming a metal layer over the conductive line.